What should a son do with his nervous mother who does not accept his words even if he is in the right? And should he leave her to her own devices?

It is recommended to be patient with one's mother and her temperament, as this is part of the obligatory righteousness and good companionship. One must avoid anything that provokes her anger and limit oneself to stating the truth calmly. If the mother does not accept it, then let her be with her opinion and do not bother to convince her with something that would provoke her anger. Allah Almighty says: (So do not say to them, "uff," and do not repel them, but speak to them a noble word.) [Al-Isra: 23]. A noble word is a soft, gentle word. The way to object to parents is to command what is right once; if they accept, then good; but if they dislike it, then one should keep silent about it and busy themselves with supplication and seeking forgiveness for them.